Variability, Stellar

Definition

Variability characterizes the changes over time of the apparent brightness of a star. Stars may exhibit long-term variations of their intrinsic luminosity, as the Sun, for instance, whose luminosity changes by about 0.1% over an 11-year solar cycle. Active stars with numerous spots present a large variability. Stars can also show a periodic variation on a shorter time scale of minutes (oscillations) to years (pulsations). The change can be dramatic as in cataclysmic variables or extremely subtle when it’s a mere oscillation. Finally, stars may also suffer partial eclipses from an orbiting companion (another star or planet). Variability is typically measured in mmag (milli-magnitudes).

Cross-References

• Activity

• Transit